Among air-conditioning apparatuses, such as multi-air-conditioning apparatuses used in a building, the following type of air-conditioning apparatus is known. By circulating a refrigerant from an outdoor unit to a relay unit and by circulating a heat medium, such as water, from the relay unit to an indoor unit, conveyance power of a heat medium, such as water, is reduced while circulating it in the indoor unit, thereby implementing a cooling and heating mixed operation (see, for example, Patent Literature 1).
The following type of air-conditioning apparatus is also known. In order to reduce the discharge temperature of a compressor, a circuit for injecting a liquid from a high-pressure liquid pipe in a refrigeration cycle into the compressor is provided in an air-conditioning apparatus. The air-conditioning apparatus can perform control so that the discharge temperature will be maintained at a temperature regardless of the operating state (for example, see Patent Literature 2).
The following type of air-conditioning apparatus is also known. R32 is used as a refrigerant and is injected from the output side of a gas-liquid separator disposed in a high-pressure liquid pipe in a refrigeration cycle into a compressor (high-pressure shell compressor) in which an air-tight container is under a discharge pressure atmosphere (for example, see Patent Literature 3).